The present invention relates to an optical head for recording and reading optical storage data and, more particularly, to a multiple channel optical head with separate write and read beams sharing a partially common optical path.
Optical storage media such as digital optical disks or digital tapes are alternatives to magnetic tape and disk memories. Optical storage offers a substantially greater data storage capacity than commercially available magnetic tape or disk memories of similar size. Optical storage media can be fixed in position within the optical writing and reading system or can be removable from the system.
A high data transfer rate is desirable in optical writing and reading systems, in addition to a large capacity for storage of data. The adoption of a multi-beam optical head has been proposed in which a plurality of writing and reading converging light beam spots are used in the optical head to obtain the high data transfer rate.
An optical head is used to write and read data on an optical recording and storage medium, which can be physically rotated or moved to allow access of various parts of the recording and storage medium to beams from the optical head.
With optical disk systems, an optical head can have separate lasers with separate optical paths for writing, reading, and tracking of the read/write laser spots on the optical recording and storage medium disk. The major advantages of such a system are good performance and versatility, while the major disadvantages are complicated optics, critical alignment, bulk and expense.
Alternately, the write laser and the read laser can be closely spaced in the optical head and share a common optical path to the optical recording medium. This provides the advantages of a compact system in size and easier alignment due to shorter optical paths.
The third choice is for the optical head to have partially common and partially separate optical paths for the write laser and the read laser to the optical recording medium. Typically the read and write lasers will share the optical path at least from the focusing object lens to the optical recording medium. In addition to a compact system in size and easier alignment, the partially shared optical path system is simpler in design and has a lower manufacturing cost.
It is an object of this invention to provide a multi-channel optical head for recording and reading optical storage data with separate write and read beams sharing a partially common optical path.
According to the present invention, the multi-channel optical head for recording and reading optical storage data has a write laser array for generating a plurality of write beams and a read laser array for generating a plurality of read beams. The write beams are information modulated beams with a relatively higher intensity while the read beams are constant magnitude beams with a lower intensity. The write beams and the read beams will not be concurrently using the optical paths of the optical head.
The write beams and the read beams share a common optical path starting with a first broadband non-polarizing beam splitter which directs the beams in the common optical path towards the optical recording medium or to a power detector. The write and read beams will be circularly polarized by a quarter-wavelength plate, pass through a second broadband non-polarizing beam splitter and then focused by an object lens onto the optical recording medium.
The write beams will record data on the moving optical storage medium, such as an optical disk or optical tape. The read beams will read the data from the moving optical storage medium and retroreflect back through the object lens to be directed by the second broadband non-polarizing beam splitter along a separate optical path. The read beams will be split by a beam splitter and focused by a focusing lens onto a detector to provide focusing information and another detector which detects its intensity to read data and provides tracking information.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.